(CNN) – The U.S. Senate on Wednesday defeated a proposed ban on semi-automatic guns modeled after military assault weapons, dealing another blow to the package of tougher firearms laws sought by President Barack Obama in the aftermath of the Newtown school massacre.

WASHINGTON, DC - APRIL 10: Sen. Pat Toomey (R-PA) (R) and Sen. Joe Manchin (D-WV) speak to the press about background checks for gun purchases, in the U.S. Capitol building April 10, 2013 in Washington DC. The pair is proposing a bipartisan compromise, a proposal to be voted on as an amendment that would expand background checks to firearms sales at gun shows and on the Internet. (Photo by Allison Shelley/Getty Images)

(CNN) – Proponents of the failed Senate amendment that called for expanding the background check system reacted with sharp disappointment Wednesday after the Senate defeated the measure in a 54-46 vote.

Meanwhile, those who opposed the amendment expressed satisfaction and pride, claiming victory for voting down a provision they claimed would infringe on Second Amendment rights.

Washington (CNN) – A man protesting new gun control measures being considered by the Senate was arrested Tuesday on the Capitol grounds when police discovered he was carrying a loaded handgun, CNN has learned.

The arrest happened at 2 p.m. on the Senate side of the plaza in front of the Capitol, according to U.S Capitol Police spokesman Officer Shennell Antrobus.FULL POST

CNN's GUT CHECK | for April 17, 2013 | 5 p.m.
– n. a pause to assess the state, progress or condition of the political news cycle

BREAKING: INCREASED BACKGROUND CHECKS FOR GUNS FAILS… The U.S. Senate just voted down a compromise proposal to expand background checks on firearms sales. The bipartisan plan was brokered by Sens. Joe Manchin, D-West Virginia, and Pat Toomey, R-Pennsylvania, and was backed by President Barack Obama in his push for a package of gun laws in the aftermath of the Newtown school massacre. – Tom Cohen

ROSE GARDEN: President Barack Obama to delivers a Rose Garden statement on the failed vote at 5:30 p.m. ET.

DEVELOPING: 'SIGNIFICANT PROGRESS,' BUT NO ARREST IN BOMBING… Authorities investigating this week's Boston Marathon attack want to question a man who was seen on video wearing a white baseball cap, two official sources with knowledge of the investigation told CNN. One of the sources said the man had the hat on backwards and was wearing a light-colored hooded sweatshirt and a black jacket. The second source said that investigators have not identified this person. – Michael Pearson and Tom Watkins

(CNN) – In a major defeat for supporters of tougher gun laws, the Senate on Wednesday defeated a compromise proposal to expand background checks on firearms sales.

The bipartisan compromise was championed by Sens. Joe Manchin, D-W.Va. and Pat Toomey, R-Pa., and backed by President Barack Obama in his push for a package of gun laws in the aftermath of the Newtown school massacre.

"On this vote, the yays are 54, the nays are 46. Under the previous order requiring 60 votes for the adoption of this amendment, the amendment is not agreed to," said Vice President Joe Biden, who presided over the vote in his role as president of the Senate.

(CNN) - Vice President Joe Biden, in his role as president of the Senate, presided over Wednesday's big vote on a a controversial amendment to the package pushed by President Barack Obama in the aftermath of the Newtown school massacre.

"I hope to God that there are 60 people up there that have the courage to stand up," Biden said during a Google+ Hangout Wednesday afternoon, before the vote.

However, the amendment, a bipartisan compromise that expands the background check system, was defeated in a 54-46 vote.

"This is going to be a close vote," he said earlier. "But I assure you one thing: If we don't get it today, we're going to get it eventually."

(CNN) - Former South Carolina Gov. Mark Sanford has engaged in a "pattern" of trespassing on his ex-wife's property since their divorce and was even issued a warning about the matter by her attorney two years ago, according to court documents related to the incident.

The Associated Press reported late Tuesday that Sanford, who is currently the Republican nominee for Congress in South Carolina's First District, has been ordered to appear in court on May 9 after his ex-wife Jenny complained that he trespassed on her Sullivan's Island property. Under the terms of their 2010 divorce, neither party can enter the other's home without permission.FULL POST

(CNN) – Republican Sen. Rand Paul of Kentucky acknowledged he made some mistakes during his speech at the historically black Howard University last week but largely defended his appearance, the first by a major Republican in nearly two decades.

At a Washington breakfast with reporters Wednesday, Paul said he was unfairly criticized by what he described as left-wing media, who argued the senator wrongly portrayed the history of African Americans switching to the Democratic Party.

In his speech last week, Paul said the transition happened during the Great Depression in the 1930s, arguing that African Americans left the GOP because they were struggling financially and weren't getting the "economic emancipation" they wanted from Republicans.

(CNN) – Mark Sanford's bid for Congress in South Carolina was dealt a major blow Wednesday when national Republicans said they would no longer support him after learning his ex-wife accused him of illegally entering her home.

"Mark Sanford has proven he knows what it takes to win elections. At this time, the NRCC will not be engaged in this special election," Andrea Bozek, a spokeswoman for the National Republican Congressional Committee, said in a statement.

The accusations of trespassing leveled at Mark Sanford, a former South Carolina governor, by his ex-wife Jenny Sanford arose after he visited his son to watch the Super Bowl.

"I did indeed watch the second half of the Super Bowl at the beach house with our 14 year old son because as a father I didn't think he should watch it alone," Mark Sanford wrote. "Given she was out of town I tried to reach her beforehand to tell her of the situation that had arisen, and met her at the back steps under the light of my cell phone when she returned and told her what had happened."

The explanation came the day after news broke Sanford has been ordered to appear in court two days after the May election in which he's contending to become South Carolina's next congressman. On Wednesday, Sanford went up with his first general election ad criticizing Democratic rival Elizabeth Colbert Busch, and a national Democratic group said it was beginning a six-figure campaign against Sanford.

Jenny Sanford claims in court documents she saw her ex-husband leaving her Sullivan's Island home on Feb. 3, roughly three weeks after Mark Sanford announced his bid for Congress.

"It's an unfortunate reality that divorced couples sometimes have disagreements that spill over into family court," Mark Sanford wrote in his statement. "I did indeed watch the second half of the Super Bowl at the beach house with our 14 year old son because as a father I didn't think he should watch it alone. Given she was out of town I tried to reach her beforehand to tell her of the situation that had arisen, and met her at the back steps under the light of my cell phone when she returned and told her what had happened."

The couple were divorced in 2010 after the then-governor admitted he was carrying on an extramarital affair with a woman from Argentina. He finished out his gubernatorial term in 2011 and has since become engaged to the same woman.

On Tuesday, Jenny Sanford wrote in a message to CNN, "I understood [the documents] were to have remained part of the sealed divorce docs. This is a private matter and I have no further comment."

Sanford said in his statement he is "particularly curious how records that were sealed to avoid the boys dealing with embarrassment are now somehow exposed less than three weeks before this election."

He said he agreed with his ex-wife that the "media is no place to debate what is ultimately a family court matter."

Seeking political redemption, Sanford won the Republican primary this month in a race to fill the 1st District seat left vacant when Gov. Nikki Haley appointed Tim Scott to the Senate late last year.

It's the same district Sanford represented in Congress before becoming governor.

As he deals with the trespassing controversy, Sanford is also going on the attack against his Democratic opponent. In his first TV commercial since he became the GOP nominee, Sanford highlights Colbert Busch's union ties.

"Elizabeth Colbert Busch says she knows jobs and will be independent, but she's not telling you that she's supported by labor unions," says the female narrator in the 30-second spot. "Nearly $30,000 in checks from big labor, even from the union who tried to shut down Boeing and ship a thousand jobs out of South Carolina."

The Sanford campaign confirms to CNN that the ad will start running Wednesday through April 22, and that the campaign will spend nearly $100,000 to run the spot on broadcast and cable television in the Charleston, South Carolina and Savannah, Georgia markets, which cover nearly all of South Carolina's 1st Congressional District. The campaign is also running the ad on radio in Charleston and Hilton Head, South Carolina.

National Journal first reported the new Sanford commercial.

Also Wednesday, a political action committee that backs Democratic House candidates, announced that it would begin a three-week, six-figure media campaign. As part of that push, House Majority PAC unveiled its first TV ad which attacks Sanford's image as a fiscal conservative.

"Mark Sanford may claim to be a fiscal conservative, but as governor he flew around the world in high style – even jetting to the dentist and a hair dresser – and stuck South Carolinians with the $400,000 bill," said House Majority PAC Communications Director Andy Stone, in announcing the new spot, titled "Air Sanford."

Sanford and Colbert Bush, sister of satirist and Comedy Central host Stephen Colbert, face off in a May 7 special election for the seat that Sanford held for three terms before being elected governor in 2002.

(UPDATE 12:49 p.m. ET)
The Capitol Police have alerted Senate staffers the situation involving a suspicious package has been resolved.

"The U.S. Capitol Police have removed the suspicious package from the Hart Senate Office Building and the envelopes from the third floors of the Hart and Russell Senate Office Buildings. The areas are now open," the agency wrote in an email.

(UPDATE 12:24 p.m. ET)
Authorities are investigating a suspicious letter at the office of Sen. Carl Levin in Saginaw, Michigan. "Earlier today, a staffer at my Saginaw regional office received a suspicious-looking letter," Levin said in a statement. "The letter was not opened, and the staffer followed the proper protocols for the situation, including alerting the authorities, who are now investigating. We do not know yet if the mail presented a threat."

(UPDATE 12:08 p.m. ET)
The man carrying a bag of letters who is being questioned by Capitol police is not believed to be connected to a letter possibly containing ricin found in a Senate mailroom and an apparently similar letter sent to President Obama, a federal law enforcement official told CNN. The man being questioned is described as emotionally disturbed, the official said.

(UPDATE 12:00 p.m. ET)
Capitol Hill Police are questioning a man with a backpack in the area of the Hart Senate Office Building. He raised suspicions with the contents of his backpack and the way he responded to police questions, two Capitol Hill police officers told CNN. The man's backpack contained sealed envelopes, one of the officers said. The backpack is being X-rayed, one of the officers said.

(POSTED 11:43 a.m. ET)
U.S. Capitol Police are evacuating the first floor of the Hart Senate Office Building due to a suspicious package. People on other floors of the building are being told to go into their offices. Separately, there is a suspicious envelope at the office of Sen. Richard Shelby of Alabama, in the Russell Senate Office Building. Security has cleared the hall but is not officially evacuating.